CVE-2025-38463

What it actually does

Signedness error in TCP skb remaining space calculation converts size_goal to unsigned before subtraction, zero-extending the result into ssize_t copy and allowing sk->sk_forward_alloc to receive a large positive value that overflows to negative on subsequent allocations.

Why it matters to the business

Linux kernel memory corruption can lead to container escapes or local privilege escalation on affected systems; high ecosystem prevalence increases exposure for cloud and server workloads, though low EPSS and no KEV status reduce immediate ransomware urgency.

How an attack unfolds

An attacker crafts TCP send operations (via TCP_REPAIR or tcp_bound_to_half_wnd reducing size_goal below skb->len) so the flawed subtraction yields an oversized copy value; tcp_wmem_schedule then wraps sk_forward_alloc around INT_MAX, enabling further memory requests to trigger negative values and memory corruption. Named threat actors including Advanced Spyware Campaign and Linux Kernel Privilege Escalation groups have targeted similar kernel memory issues in container environments.

How to fix it

Apply the upstream fix in commit 81373cd1d72d87c7d844d4454a526b8f53e72d00; rebuild and deploy the patched kernel across all affected Linux distributions and container hosts.

How to confirm the fix worked

Verify the running kernel contains commit 81373cd1d72d87c7d844d4454a526b8f53e72d00 or later equivalent; inspect /proc/version or kernel build logs for the fix hash and re-run syzkaller reproducer to confirm absence of overflow.

Typical attack path

1. Establish TCP connection and prepare write queue with existing skb
2. Trigger condition via TCP_REPAIR or tcp_bound_to_half_wnd to make size_goal < skb->len
3. Perform send that executes flawed copy = size_goal - skb->len arithmetic
4. Allow tcp_wmem_schedule to set sk_forward_alloc near INT_MAX
5. Issue additional allocations that cause wrap to negative and corrupt kernel memory structures

How to detect it

Search kernel logs and audit records for TCP_REPAIR socket operations followed by large memory allocation failures; correlate with container breakout attempts or privilege escalation traces reported by threat actors exploiting analogous kernel memory flaws.

What your security team should do

• Prioritize kernel upgrades to the fixed commit on all production and container hosts within the next maintenance window
• Monitor EPSS trend and threat actor activity for any increase in exploitation attempts against similar memory issues
• Harden container runtimes with seccomp and user namespaces to limit impact of kernel memory corruption
• Include the fixed commit in golden images and CI build pipelines